Silver has a very strong catalytic effect on the peroxodisulphate oxidation of Brilliant Cresyl Blue in the presence of 1.10-Phenanthroline as an activator. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance of brilliant cresyl blue at 635 nm and 30°C. Silver can be determined in the range of 0.3 – 1500.0 ng/ml by a fixed time method. The limit of detection is about 0.1 ng/ml of silver. Silver in real samples was determined with satisfactory results.